Protective helmet



FIG. 1 is a front view of a protective helmet, showing my new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof; and,

FIG. 6 is a perspective view thereof.

The broken lines shown in the figures form no part of the claimed design. 

CLAIM The ornamental design for a protective helmet, as shown and described. 